1. Field of the Invention
The present invention relates to a multi-output determination circuit that determines whether or not the levels of plural input signals are equal to or higher than an upper-limit value or equal to or lower than a lower-limit value.
2. Description of the Related Art
In electric vehicles such as electric cars and hybrid cars, a DC high voltage from a high-voltage battery is converted to an AC voltage, e.g. a three-phase AC voltage, by an inverter and a drive source electric machine is rotated by this three-phase AC voltage to thereby obtain the drive source of vehicle travelling. Furthermore, a hybrid vehicle is a car that employs a motor in addition to an engine as the drive source of its travelling, and the motor is driven to assist the engine and carry out regenerative braking of the motor.
In order to drive the motor with the optimum torque, based on the target torque, the U-, V-, and W-phase command voltages that should be applied to the motor are calculated from the detected values of the U-, V-, and W-phase currents detected by a phase current detection sensor and the motor angle detected by a motor angle readout sensor, and the motor is driven by PWM control via the inverter.
At this time, if the detected motor rotation angle is different from the actual angle because of a system malfunction attributed to e.g. the failure of the motor angle readout sensor, the phase voltages are applied to the motor and the motor is driven in the state in which the inductance of the armature of the motor is lower than the target inductance. Thus, an overcurrent flows to the motor. In addition, an overcurrent flows to the motor also because of a system malfunction attributed to trouble with a CPU (hardware and software) for controlling the motor. If an overcurrent flows, the motor temperature is increased and the motor is possibly damaged. Therefore, it is necessary to detect the overcurrent and stop the motor.
Examples of the related art for detecting the overcurrent of the motor include Japanese Patent Laid-Open No. Sho 64-19914 and Japanese Patent Laid-Open No. She 64-039227. The following configuration is described in Japanese Patent Laid-Open No. Sho 64-19914. Specifically, the current flowing to the motor is detected by the current detection circuit 22 provided in the inverter main circuit. Furthermore, a low-level overcurrent due to e.g. motor lock is detected by the low-level current detection circuit 4, and an overcurrent due to e.g. short-circuiting is detected by the high-level current detection circuit 5. If an overcurrent is detected, the motor is stopped.
The following configuration is described in Japanese Patent Laid-open No. 64-039227. Specifically, the short-circuiting of the arm of the inverter is detected by the DC converters 9-1, 9-2, and 9-3 for the U-, V-, and W-phases, and comparisons with reference voltages are made by the comparators 17-1, 17-2, and 17-3 to thereby detect whether or not short-circuiting has occurred, so that protection against short-circuiting is achieved.
However, in Japanese Patent Laid-Open No. Sho 64-19914, in which a low-level overcurrent due to e.g. motor lock is detected by the low-level current detection circuit 4 and an overcurrent due to e.g. short-circuiting is detected by the high-level current detection circuit 5, in order to protect the motor against a system malfunction, an overcurrent is detected for the U-, V-, and W-phases. In addition, in the case of making comparisons with reference voltages, the comparison with the reference voltage needs to be made for each phase by the comparators, and therefore six comparators are required. Thus, the number of comparators is large, which leads to a problem that the cost is high.
Furthermore, in Japanese Patent Laid-Open No. Sho 64-039227, the comparisons with the reference voltages need to be made by the comparators in order to detect short-circuiting for each of the U-, V-, and W-phases. This also causes a problem that the number of comparators is large and therefore the cost is high.